Package com.badlogic.gdx.utils

Class IntSet

java.lang.Object

com.badlogic.gdx.utils.IntSet

public class IntSet
extends java.lang.Object

An unordered set where the items are unboxed ints. No allocation is done except when growing the table size.

This class performs fast contains and remove (typically O(1), worst case O(n) but that is rare in practice). Add may be slightly slower, depending on hash collisions. Hashcodes are rehashed to reduce collisions and the need to resize. Load factors greater than 0.91 greatly increase the chances to resize to the next higher POT size.

Unordered sets and maps are not designed to provide especially fast iteration. Iteration is faster with OrderedSet and OrderedMap.

This implementation uses linear probing with the backward shift algorithm for removal. Hashcodes are rehashed using Fibonacci hashing, instead of the more common power-of-two mask, to better distribute poor hashCodes (see Malte Skarupke's blog post). Linear probing continues to work even when all hashCodes collide, just more slowly.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	IntSet.IntSetIterator

Field Summary

Fields

Modifier and Type	Field	Description
protected int	mask	A bitmask used to confine hashcodes to the size of the table.
protected int	shift	Used by place(int) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask).
int	size

Constructor Summary

Constructors

Constructor	Description
IntSet()	Creates a new set with an initial capacity of 51 and a load factor of 0.8.
IntSet(int initialCapacity)	Creates a new set with a load factor of 0.8.
IntSet(int initialCapacity, float loadFactor)	Creates a new set with the specified initial capacity and load factor.
IntSet(IntSet set)	Creates a new set identical to the specified set.

Method Summary

Modifier and Type	Method	Description
boolean	add(int key)	Returns true if the key was added to the set or false if it was already in the set.
void	addAll(int... array)
void	addAll(int[] array, int offset, int length)
void	addAll(IntArray array)
void	addAll(IntArray array, int offset, int length)
void	addAll(IntSet set)
void	clear()
void	clear(int maximumCapacity)	Clears the set and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.
boolean	contains(int key)
void	ensureCapacity(int additionalCapacity)	Increases the size of the backing array to accommodate the specified number of additional items / loadFactor.
boolean	equals(java.lang.Object obj)
int	first()
int	hashCode()
boolean	isEmpty()	Returns true if the set is empty.
IntSet.IntSetIterator	iterator()	Returns an iterator for the keys in the set.
boolean	notEmpty()	Returns true if the set has one or more items.
protected int	place(int item)	Returns an index >= 0 and <= mask for the specified item.
boolean	remove(int key)	Returns true if the key was removed.
void	shrink(int maximumCapacity)	Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less.
java.lang.String	toString()
static IntSet	with(int... array)

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

size

public int size

shift

protected int shift

Used by place(int) to bit shift the upper bits of a long into a usable range (>= 0 and <= mask). The shift can be negative, which is convenient to match the number of bits in mask: if mask is a 7-bit number, a shift of -7 shifts the upper 7 bits into the lowest 7 positions. This class sets the shift > 32 and < 64, which if used with an int will still move the upper bits of an int to the lower bits due to Java's implicit modulus on shifts.

mask can also be used to mask the low bits of a number, which may be faster for some hashcodes, if place(int) is overridden.

mask

protected int mask

A bitmask used to confine hashcodes to the size of the table. Must be all 1 bits in its low positions, ie a power of two minus 1. If place(int) is overriden, this can be used instead of shift to isolate usable bits of a hash.

Constructor Detail

IntSet

public IntSet()

Creates a new set with an initial capacity of 51 and a load factor of 0.8.

IntSet

public IntSet(int initialCapacity)

Creates a new set with a load factor of 0.8.

Parameters:

initialCapacity - The backing array size is initialCapacity / loadFactor, increased to the next power of two.

IntSet

public IntSet(int initialCapacity,
              float loadFactor)

Creates a new set with the specified initial capacity and load factor. This set will hold initialCapacity items before growing the backing table.

Parameters:

initialCapacity - The backing array size is initialCapacity / loadFactor, increased to the next power of two.

IntSet

public IntSet(IntSet set)

Creates a new set identical to the specified set.

Method Detail

place

protected int place(int item)

Returns an index >= 0 and <= mask for the specified item.

The default implementation uses Fibonacci hashing on the item's Object.hashCode(): the hashcode is multiplied by a long constant (2 to the 64th, divided by the golden ratio) then the uppermost bits are shifted into the lowest positions to obtain an index in the desired range. Multiplication by a long may be slower than int (eg on GWT) but greatly improves rehashing, allowing even very poor hashcodes, such as those that only differ in their upper bits, to be used without high collision rates. Fibonacci hashing has increased collision rates when all or most hashcodes are multiples of larger Fibonacci numbers (see Malte Skarupke's blog post).

This method can be overriden to customizing hashing. This may be useful eg in the unlikely event that most hashcodes are Fibonacci numbers, if keys provide poor or incorrect hashcodes, or to simplify hashing if keys provide high quality hashcodes and don't need Fibonacci hashing: return item.hashCode() & mask;

add

public boolean add(int key)

Returns true if the key was added to the set or false if it was already in the set.

addAll

public void addAll(IntArray array)

addAll

public void addAll(IntArray array,
                   int offset,
                   int length)

addAll

public void addAll(int... array)

addAll

public void addAll(int[] array,
                   int offset,
                   int length)

addAll

public void addAll(IntSet set)

remove

public boolean remove(int key)

Returns true if the key was removed.

notEmpty

public boolean notEmpty()

Returns true if the set has one or more items.

isEmpty

public boolean isEmpty()

Returns true if the set is empty.

shrink

public void shrink(int maximumCapacity)

Reduces the size of the backing arrays to be the specified capacity / loadFactor, or less. If the capacity is already less, nothing is done. If the set contains more items than the specified capacity, the next highest power of two capacity is used instead.

clear

public void clear(int maximumCapacity)

Clears the set and reduces the size of the backing arrays to be the specified capacity / loadFactor, if they are larger.

clear

public void clear()

contains

public boolean contains(int key)

first

public int first()

ensureCapacity

public void ensureCapacity(int additionalCapacity)

Increases the size of the backing array to accommodate the specified number of additional items / loadFactor. Useful before adding many items to avoid multiple backing array resizes.

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object obj)

Overrides:

equals in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

iterator

public IntSet.IntSetIterator iterator()

Returns an iterator for the keys in the set. Remove is supported.

If Collections.allocateIterators is false, the same iterator instance is returned each time this method is called. Use the IntSet.IntSetIterator constructor for nested or multithreaded iteration.

with

public static IntSet with(int... array)